Predictive Multi-scale Modeling of Shape-Selective Adsorption and Reaction in Acid/Base Zeolite Biofuel Catalysts

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

0932777 Auerbach Intellectual Merit: Objectives: The PI will continue developing and applying methods of theoretical chemistry to assist in the design of zeolites as biofuel and bioproduct catalysts. In previous work, he has modeled the spectroscopic signatures and formation/stability kinetics of nitrogen-containing zeolites X/Y/ZSM5 - i.e., zeolites with some bridging oxygens replaced with bridging amine (-NH-) groups - which show promise as shape-selective base catalysts for biofuel production. In this work he will continue study of nitrogen-containing zeolites by directly modeling size- and shape-selectivity of aldol condensation (a carbon-carbon bond forming reaction) in both acidic and basic zeolites X/Y/ZSM5, to identify how zeolite chemistry impacts catalyst selectivity and activity. In a new direction, he will perform cutting-edge modeling to investigate size- and shape-selective adsorption in these zeolites under the high-temperature conditions of catalytic fast-pyrolysis (CFP), a process that Huber has shown converts cellulose directly into biofuels. He will quantify thermal distortions of the sizes and shapes of zeolite pores, and how such distortions impact adsorption and diffusion of relevant biofeeds and biofuels. Approaches: (i) Aldol Condensation: The PI will model the aldol condensation of furfural (C5) and acetone (C3) to the C8 product (so-called "monomer"). He will also model an additional condensation of C8 monomer and furfural to a C13 "dimer" product. Such reactions are promising routes for upgrading biomass-derived feeds into gasoline-range fuels. He will learn how to tune the monomer/dimer selectivity by computing the reaction pathways in medium-pore (ZSM5) and large-pore (X/Y) zeolites. He will learn how to tune activities by modeling these reactions in both acidic and basic versions of these zeolites. Electronic energies will be computed using embedded cluster (QM/MM) techniques; complex reaction pathways will be discovered using the "climbing image nudged-elastic band" method, which he has recently implemented in an efficient way with the Gaussian computational chemistry program. (ii) High-temp Adsorption: The PI will perform periodic electronic structure calculations with various unit cell sizes to parameterize a new forcefield that reproduces zeolite thermal expansion. Using this new forcefield, he will perform statistically rigorous constant-pressure simulations to determine how zeolite distortions may accommodate the adsorption of relatively large molecules such as glucose and levoglucosan, and the formation of relatively large species such as naphthalene, during CFP. Scientific Impacts: The PI's computational studies of aldol condensation will shed light on how to exploit the shape-selective properties of zeolite catalysts to produce biofuels of desired lengths. His work will directly impact, and will benefit from, collaboration with the Huber group at UMass (see support letter), which is experimentally studying these same reactions. His modeling of high-temperature adsorption will help to explain whether CFP products such as naphthalene are formed inside or outside of zeolites, providing the insights necessary to further improve and optimize CFP. This project will directly impact, and benefit from, our collaboration with the Grey group at SUNY Stony Brook (see support letter), which is using X-rays to measure zeolite expansion. Broader Impacts: The PI will continue to recruit under-represented students to this program, exploiting existing NSF-funded REU and NEAGAP programs at UMass. He will continue to collaborate with the Center for Talented Youth to engage in middle-school outreach using Biofuels as the hook for young minds. The PI will deliver an undergraduate course on Renewable Energy in Fall 2009, in which Biofuels will play a prominent role. In parallel, the PI is leading a committee at UMass to develop a new interdisciplinary concentration (like a minor) on Renewable Energy. This proposal will support undergraduate research as a capstone experience of the Renewable Energy concentration.